According to Goldman’s Jim O’Neill, who’s opinion I normally respect.

“Perhaps the markets are right to look through some of the ongoing concerns about a number of the smaller countries and disregard whether they stay or go,” he said. “Following this line of reasoning, since the combined weight of Greece and Portugal in the euro area is less than 5%, it may not be a big deal if they leave.”

Based on their tiny contribution to euro zone GDP, Greece leaving means nothing. But that’s not the point, and never has been.

The point of the euro zone was that it is the precursor to a united states of Europe, a federal government with one fiscal and monetary system. It was meant to be a permanent arrangement that could be added too, but not subtracted from…

So here is the problem for the euro zone. If Greece leaves, who’s next?

Ireland? Small country, who cares…

Portugal? Ditto.

Spain? Wait a minute!

Netherlands? Whoa, hold on now…

That’s the problem for the euro. It is only as good as its weakest link, and there are plenty of weak links, at the moment. To mix a metaphor, once the dominoes start falling, there is no telling where (or if) they stop.